Though it's unclear if the rats come with paperwork, a search of ratbehavior.org shows that that particular kind of rat can grow 16 inches long. And they are very aggressive, "fighting, chasing, biting and boxing."

While the Iranians have used poison to kill the rats during the daytime, at night the teams of sharpshooters use infrared lenses to hunt them down.

"We have identified the rats' places of congregation by using (computer) software," Heydarzadeh explained.

By the end of 2013, the Iranians hope to have 40 teams of shooters working, he added.

So far, 2,205 rats have been killed. Their bodies are carted off and incinerated or buried in special dumps, the environmental official explained.

University researchers are working with the government to assess whether their newest plan of attack is working.

But Heydarzadeh feels good.

"The number of these rodents in Tehran," he said, "is on the decline."